I Need Some Help, My Colf Officers Enhanced developed a Stain

[zebraranger]

First I'd like to say hello to everyone, Its been a little while since I've been here. This is my situation, I decided to go through the safe and oil down my handguns and rifles, I do this on a pretty regular basis, whether I've been shooting or not. I keep the humidity level between 39% & 41% in the safe, which can be tough here in Florida where humidity gets to 100% a lot of the time. I have a dehumidifier in there along with a Rustblocker safe VPCI emitter. I always clean and oil them after every use before putting them back in the safe and have never had a problem. After doing all this, I noticed this stain on the back of my stainless Colt Officers Enhanced .45acp. Dont have any idea how it got there, Its located on the back side of the grip just under the grip safety. Looks like its spreading to the right a little. I used a tooth brush and some CLP to get into the grooves and it didnt remove it. I also used some stainless steel cleaner, and nothing. I've looked at it through a magnafying glass and its not rust, just looks like dark discoloration. Looks like its in the steel, but I have never seen this before, Im concerned it might get worse. Any ideas? Here's a couple of Photo's, 2nd one shows the stain. Any input would be appriciated.
http://i204.photobucket.com/albums/bb204/zebraranger/DSC03521.jpg
http://i204.photobucket.com/albums/bb204/zebraranger/DSC05400.jpg

[egumpher]

Interesting.

This main spring housing is plastic (glass fill nylon just like Glock and other plastic pistol frames) so imagine that you need something that will extend info the serration to clean them. I use the tip of a pocket knife blade to clean the main spring housing on my Lightweight Commander which is exactly the same as your picture. I Just scrape it clean.............I doubt that you contaminated it with anything that could discolor this type plastic.

BTW a new MSH is about $10 from Colt.

Rgds
Eric